1. Field of the Invention
The present invention relates to a multi inlet valve internal combustion engine and more specifically to an inlet port arrangement for such an engine which reduces the wetting of the spark plug electrodes during low engine temperature and/or idling operation.
2. Description of the Prior Art
FIG. 1 shows a prior art multi inlet valve type engine of the nature disclosed in Japanese Patent Application First Provisional Publications Sho59-93926, 59-105925 and 59-105926. In these arrangements two inlet valves 1,2 and one exhaust valve 3, are arranged to control the communication between the induction and exhaust systems and each combustion chamber. However, these arrangements encounter the problem that when the engine temperature is low and/or the engine is idling, the fuel passing through the induction system tends to be poorly carburetted and the air-fuel mixture contains a large amount of unvaporized liquid fuel. Accordingly, as the inlet valve 2 is opened before valve 3 (by a suitable valve train) under such conditions and the section 5 of the bifurcate or so called siamesed port 6 which is associated with valve 2 is designed to direct the flow of air fuel mixture into the combustion chamber in a manner to swirl therearound, the liquid fuel contained in the charge tend to carried toward and impinge on the electrodes of the spark plug 6. This of course wets the plug and hampers efficient ignition of the air-fuel mixture, destablizes engine operation and invites notable increases in HC emissions under such conditions.